150 



Diseases of Poult ry 



function is performed by the sweat glands and the secretion 

 of the kidneys. Birds have no sweat glands and the secre- 

 tion of the kidneys contains relatively little moisture. 



The air passages are lined with mucous membrane and this 

 membrane is the seat of several diseases. Diseases are easily 



Fig. 28. — .Cross section of two of the small air tubes of the lung of a goose. 

 On the right the air passages are filled with black injection mass. On 

 the left the arteries are similarly injected. (From Oppel, after Schulze.) 



transferred from one part of the respiratory system to another, 

 since the passages and also the lining membranes are contin- 

 uous from the nostrils to the air sacs. There are also diseases 

 of the vascular part of the lungs. Some of these diseases are 

 caused by unfavorable conditions as exposure to cold, 

 drafts of air, or moist air or to improper food. Others 

 are due to specific organisms. Most of the latter are con- 

 tagious. Exposure to unfavorable conditions also reduces 

 the ability of the birds to resist infectious diseases. 



